News Release Distributed 11/09/12BATON ROUGE, La. – An apparent increase in cases of hemorrhagic disease among deer in the Florida parishes of Louisiana has caused concern among hunters and wildlife experts. But that doesn’t mean the disease is on the rise, according to an entomologist with the LSU AgCenter.
Hemorrhagic disease in deer is recognized as a fall disease, said Lane Foil, who holds the Pennington Chair for Wildlife Research in the LSU AgCenter.
“You can find some pockets of outbreaks in most years,” Foil said. “But because hemorrhagic disease is sporadic is Louisiana, it can be more of a local and intense problem when it occurs.”
A widespread outbreak of hemorrhagic disease is called an epizootic, which is the term applied to animals equivalent to epidemic in people. Survivors of the disease have immunity, but maybe not for life, Foil said. “In some years, the epizootics in Louisiana are more dramatic than in other years.”
The epizootic in Louisiana has been particularly evident in 2012 because Hurricane Isaac and the consequent flooding increased deer density in the areas unaffected by high water. “The larger concentrations of animals are more likely to be infected because midges find them easier,” Foil said.
That was likely the case this year, and hunters and land managers have reported more dead dear than in previous years.
Foil has been conducting research on the disease at the Wildlife Research Institute at the LSU AgCenter Bob R. Jones-Idlewild Research Station in Clinton. The station provides a unique opportunity to study the disease because it has captive herds of white-tailed deer and red deer along with cattle and wild deer on the 1,800-acre facility.
Hemorrhagic disease comes in two forms caused by two viruses – the blue tongue virus and the epizootic hemorrhagic disease virus, known by its initials EHDV. The viruses are in the genus orbivirus, which includes 22 species and at least 130 different serotypes or subspecies, Foil said.
Foil conducts blood tests on all the cattle and captive deer on the research station each year to monitor the presence of the viruses.
Orbiviruses can infect and replicate within a wide range of insects and mammals. The ones Foil is studying may infect deer, cattle, sheep and goats.
While cattle seldom display clinical symptoms, deer, on the other hand, are sensitive to the viruses. In addition to monitoring the AgCenter deer herds, Foil is testing deer harvested in managed hunts for prior exposure to hemorrhagic disease viruses.
“As far as we know, the primary method of transmission is insects – in particular the biting midge Culicoides sonorensis,” Foil said.
The virus has to reproduce in the midge before it can be transmitted to another animal. The insect bites infected animals and takes in the virus, which replicates in the midge, which can take about a week. Then the midge bites another animal and transmits the virus.
In some areas of the country, transmission of the viruses is widely prevalent almost every year. In these areas, “continual exposure from consistent transmission gives a continual ‘booster’ effect to the animal population and helps the animals maintain a level of immunity,” Foil said.
Hemorrhagic disease is of particular concern for managed deer farms, of which Louisiana has between 200 and 400. The results of Foil’s research can help them maintain and improve their operations, “which is important because managed, captive deer herds are economically important,” he said.
Foil is researching how the midge behaves and examining disease transmission in “intensive agricultural situations as well as in the wild deer populations.”
“What we learn will help explain what’s happening,” he said. “We want to develop management activities to control epizootics.
“Culicoides sonorensis is an insect so well known that we know the larval habitats,” Foil said. “They exist in environments around intensive animal husbandry.”
Managing larval habitats will help manage the disease, he said. “Management may be different with intensive farming when compared with the ‘big wild herd’ in Louisiana.”
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